Pressure compensated air throttle and air-fuel control system

ABSTRACT

An air throttle is disclosed which meters a constant airflow for each control position over the range of manifold vacuums encountered in engine operation. Throttle metering area is the product of two perpendicular openings, an x-opening proportional to desired airflow and a y-opening controlled as a function of manifold vacuum to compensate throttle area for variations in manifold vacuum so that airflow for a given x-opening is constant or a desired function over the range of manifold vacuums. If flow per unit area is a function of intake manifold vacuum g(IMV) the y-opening of the throttle is proportional to 1/g(IMV) to maintain constant airflow at a given control setting x. If fuel flow is controlled proportionately to x and an air-fuel ratio function h(IMV) is desired, the throttle will produce it with a y-opening controlled to vary in proportion with h(IMV)/g(IMV).

Showalter et al.

1111 3,815,562 1 June 11, 1974 PRESSURE COMP ENSATED AIR THROTTLE ANDAIR-FUEL CONTROL SYSTEM Inventors: Merle Robert Showalter, 4733Shoremead Rd., Richmond, Va. 23234; Samuel Rhine, RFD 424A, Tillson, NY.12486 Filed: Mar. 8, 1973 Appl. No.: 339,156

US. Cl...... 123/119 R, 123/139 AW, 123/100,

123/106 Int. Cl. F02m 39/00, F02b 3/00, F02m 23/00 Field of Search123/119 R, 139 AW 8/1960 Dietrich 8/ I 971 Nambu... .1 123/139 AWPrimary Examiner-Wendell E. Burns Attorney, Agent, or FirmWitherspoonand Lane ABSTRACT An air throttle is disclosed which meters a constantairflow for each control position over the range of manifold vacuumsencountered in engine operation. Throttle metering area is the productof two perpendicular openings, an x-opening proportional to desiredairflow and a y-opening controlled as a function of manifold vacuum tocompensate throttle area for variations in manifold vacuum so thatairflow for a given x-opening is constant or a desired function over therange of manifold vacuums. If flow per unit area is a function of intakemanifold vacuum g(1MV) the yopening of the throttle is proportional tol/g(1MV) to maintain constant airflow at a given control setting x, Iffuel flow is controlled proportionately to x and-an air-fuel ratiofunction h(lMV) is desired, the throttle willproduce it with a y-opening controlled to vary in proportion with h(1MV)/g (lMV).

9 Claims, ll'Drawing Figures 7/ ll/I111. 4

PATENTEBJUM 1 m4 SHEET 10F 3 SONIC QUMV) (AIRFLOW) I6 CRITICAL IMV FIGla.

PRESSURE COMPENSATED AIR THROTTLE AND AIR-FUEL CONTROL SYSTEM BACKGROUNDAND OBJECTS In injection carburetors and injection systems for throttledinternal combustion engines, it is necessary to control air-fuel ratioclosely and this results in many problems in the design of thesesystems. In the past, it

has generally been the practice to throttle the airflow with aconventional butter-fly valve, and to either measure airflow through aventuri meter or calculate it in some way as a function of intakemanifold vacuum, lMV, and engine RPM to actuate a control on fuel flowto secure the desired air-fuel ratio. The result has been somecomplexity in the fuel metering arrangement to overbalance thesimplicity of the air throttle.

It is a purpose of the present invention to provide an air throttlewhich meters a constant airflow (or a desired air-flow function) foreach throttle control position over the range of manifold vacuumsencountered in engine operation so that the pressure compensatedthrottle will automatically produce the desired air-fuel ratio functionwhen used in conjunction'with a fuel flow system where fuel flow islinear with control position and invariant with intake manifold vacuum.It is a further purpose to provide a pressure compensated throttlewhich, used in conjunction with a linear fuel flow device, is readilyadaptable to supplementary airfuel ratio control as a desired functionof RPM, air temperature, engine temperature, altitude, and otherparameters if necessary.

It is yet another purpose of the present invention to produce a throttlevalve which is readily adaptable to injection of fuel directly below theair throttle to takeadvantage of thevery high velocity flow (which isgenerally sonic velocity flow during engine operation) for fuelatomization.

It is another purpose of the present invention to provide an airthrottle which requires a negligible manifold pressure drop fromatmospheric-pressure for efficient high power operation.

These and other objects are attained by an air throttle where throttlearea is proportional to the product of two perpendicular openings, anx-direction opening proportional to desired airflow and positivelylinked to desired fuel flow, and a y-direction opening controlled as afunction of manifold vacuum to compensate throttle area to produce thedesired airflow per unit xopening as a function of intake manifoldvacuum. The viscosity of air is so low that its flow through aknifeedged orifice is frictionless shear flow to an adequateapproximation; therefore, flow per unit throttle area can be expressedas a function of intake manifold vacuum g(lMV).

Airflow through the metering throttle is a function of intake manifoldvacuum, IMV, throttle flow cross sectional area, A, and a characteristicflow constant k:

f lgu A if throttle cross section A is the product of an xopening and aY-opening controlled as a function of vacuum IMV, airflow per unitx-opening is constant regardless of IMV if y is inversely proportionalto g (IMV):

f= k,g(lMV) (k /g(lMV)) .r reduces to f= k, k x for all IMV.

If the y-opening of the rectangular throttle is controlled by adiaphragm with one side at manifold pressure and the other side atatmospheric pressure and with a spring on the intake pressure side sowound that the diaphragm controls the throttle y-opening to beproportional to the reciprocal of g(IMV), airflow through the throttlewill be proportional to the throttle x-opening and invariant with intakemanifold vacuum.

If it is desired to maintain the engines air-fuel ratio constant, it issufficient to control the y-opening proportional to l/g( lMV), but it isgenerally desired to control air-fuel ratio as a function of intakemanifold vacuum. 'If the air-fuel metering system is designed so thatfuel flow and the x position of the throttle always varyproportionately, a variable air-fuel ratio function of manifold vacuumh(lMV) will be generated by the system if the y-opening of the throttleis controlled to be proportional to h(IMV)/g(lMV).

Airflow per unit flow'cross section can be adequately approximated as afunction g(lMV) becauseairflow is a weak enough function of atmospherictemperature changes and expected variations in operating altitude forautomobiles, and the function g(lMV) can be adequately compensatedforthese variations to provide air metering to any required degree ofaccuracy. 1

Airflow through a properly designed (knife edged) air throttle is to anexcellent approximation a frictionless isentropic flow from a reservoirat atmospheric pressure to intake manifold pressure. For subsonic flows:

A flow cross section of throttle P reservoir (atmospheric) pressure Pthrottle back pressure (absolute manifold pressure) p reservoir(atmospheric) density 'y c,,/c,. the ratio of specific heat at constantpressure to specific heat at constant volume.

Maximum flow per unit cross sectional area A occurs at sonic velocity,where:

\ [Z'Y/(Y 0Po] A m (2/'y l) for air, y 1.4 and (4.7.14) reduces to m0.684 (P p A accuracy is required, and the spring or servo setting of k/g(lMV) can be a simple function of intake manifold vacuum, P P.

The desired air-fuel ratio function, h, for a particular engine is ingeneral a functionof atmospheric pressure P,,, manifold pressure P, RPM,intake air temperature, engine temperature, and other parameters such asexhaust back pressure, fuel density, fuel hydrogen-carbon ratio, etc.However, in practice the airfuel ratio function is a function of onlysome of these parameters, of which intake manifold vacuum is always oneh(IMV, An air-fuel ratio function of the following form will operatesatisfactorily:

where:

xlfuel= k hm. h (P,,, T, h.,(RPM) and the air throttle y-opening y=[muMvvguMvn since throttle area A is proportional to the xopening timethe y-opening. This variation of y as a function of IMV can be attainedby a control consisting of a diaphragm with one side at manifoldpressure and the other side at atmospheric pressure actuating theyopening where the spring on the diaphragm is so wound that they-opening of the air throttle is proportional to h,(IMV)/g(IMV).

Under some conditions, a degree of accuracy so great that the effect ofviscosity on airflow cannotbe ignored may be required and is probablybest to plot g(IMV) empirically rather than theoretically. The effect ofviscosity will be to produce relatively less airflow when the throttleis nearly closed, causing a relative enrichening of fuel-air ratio atlow engine power and a relative enleanment at high engine power. Thismay even be desirable, and some intermediate value g(IM\ function may bebuilt into the throttle system. Alternatively, the open area of the airthrottle may be covered by a screen so that the relative edge effectwill become very small with relation to the viscous drag of the screen.This will make the g(IMV) function valid throughout the flow range (fora fine mesh screen), simply reducing the coefficient of discharge of thethrottle orifice without changing the shape of the flow function fromthe isentropic form mentioned previously.

Beyond a certain level of complexity of h(lMV,

it becomes worthwhile to use a computer air-fuel ratio control analogousto the electronic computer control systems now used with certain fuelcontrols. Even in this case, it is advantageous to control fuel using asimple linear fuel flow control and control air-fuel ratio as a desiredfunction of engine parameters by varying I tle.

the air throttling area as a function of manifold vacuum and otherparameters. In this manner, the control actuator need only move slowly(as opposed to solenoid injection valves). and the simplicity of fuelmetering across a constant pressure drop can be used to advantage. Thisscheme is compatible with any desired accuracy and complexity ofair-fuel ratio control.

IN THE DRAWING FIG. I is a graph representing the function g(IMV).

FIG. la is a graph representing one possible function h(IMV).

FIG. 2 is a schematic of the throttle in combination with a simplelinear fuel flow control; the combination forms an engines air-fuelcontrol.

FIG. 3 shows a rectangular throttle iris on a manifold.

FIGS. 3a, 3b, 3c and 3a show exemplary shapes for the variable area airthrottle.

FIG. 4 shows a linkage for the variable area air throt- FIG. 4a'is asectional view taken along line la-4a of FIG. 4 showing the desirableedge shape of the plates.

FIG. 5 is a schematic of an iris computer controlled throttle incombination with a simple linear fuel flow control.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 plots g(IMV) airflow perthrottle opening cross sectional area for a knife; edged orifice airthrottle, and is characteristic for air. Note that flow rates increaserapidly between 0 IMV and 2"I-Ig IMV, where flow is already about halfof sonic velocity, and flow increases approximately as the square rootof IMV until sonic velocity is reached at the critical IMV. Since g(IMV)is constant at sonic velocity above critical IMV, any change in the yopening proportional to h(IMV)/gIMV) above critical IMV is due tovariation in h(IMV) in this high vacuum range. Note that engines undernormal operating conditions spend the great majority of time withairflow rates which are nearly sonic or sonic. The energy contained inthis high velocity airstream can be used to produce excellentatomization, as will be discussed later.

FIG. la represents one of the many possible h(IMV) functions which canbe programmed into the air throttle air-fuel ratio control system. Theh(IMV) function operates lean within the normal loaded range of IMV forfuel economy and NO and CO control, richening for very low manifoldvacuums so that maximum engine power is obtainable, and also richeningat the relatively high vacuums where flame propagation requires a richermixture than is required in the middle IMV range. Other h(IMV) functionscan, of course, be substituted for the one shown in FIG. 1a depending onthe detailed design requirements of the engine the system is to bematched with. I

FIG. 2 shows a schematic of the throttle invention in combination with afuel'control system designed so that fuel flow is proportional to thex-opening of the x-y rectangular iris air throttle. Opening and closingiris plates 1, 2, 3 and 4 are mounted on passage 5 which is the intakepassage of 'an automobile engine (not shown). The chamber in passage 5is at intake manifold. pressure. Plates 3 and 4 open and close togetherand the distance between them is the x-opening of the air throttle.Plates 1 and 2 open and close together and the distance between themforms the y-opening of the air throttle. The opening and closing ofy-plates l, 2 is controlled by a linkage 11 to a spring loaded diaphragmassembly 12a which controls the y-opening of plates 1, 2 to beproportional to h(lMV)/g(IMV). Diaphragm 6 opens and closes y-plates 1,2 through linkage 11 and moves to balance the differential pressureacross diaphragm 6 with the spring tension of calibrated spring 7, whichspring is mounted in compression between diaphragm 6 and mount 8. Stop12 constrains the maximum travel of diaphragm 6 towards mount 8. Linkage11 serves to open and close y-plates 1, 2 in response to the interactionof 11 and spring loaded diaphragm assembly 12a so that the y-openingbetween plates 1, 2 is proportional to h(IMV)/g(lMV) as required.

Fuel is introduced into the high velocity airstream below the throttleby means of a pintle nozzle 13 of the V type disclosed by RobertShowalter in copending U.S.

Pat. application Ser. No. 126,179 filed Mar. 19,1971 where fuel ismaintained as a pressurized liquid prior to ejection through pintlenozzle 13 and is heated to a temperature where its vapor pressure issubstantially in excess of the pressure in chamber 5 so that the fuelejected from nozzle 13 immediately flashes to vapor and micronicstable'aerosol droplets. Fuel is heated to the required temperatureprior to passing to nozzle 13 in line 14, which is heated inside heatpipe fuel heater 15, which maintains the fuel in line 14 within a narrowdesired temperature range. Heat pipe fuel heater 15 is heated by anevaporator section in the exhaust passage 16 of an automobile engine.Other assemblies for introducing fuel into the engine could besubstituted for the one shown, including continuous or pulsed fuelinjection systems and simpler nozzle assemblies, for use in conjunctionto the pressure compensated air throttle.

Note that any nozzle or fuel introduction means in the position ofnozzle 13 is in a sonic or nearly sonic airstream. This sonic airstreamwill break up fuel into droplets of the order of 10 microns even whenfuel is cold for simpler fuel introduction nozzles. The substantialatomization energyin the high velocity airstream downstream from thethrottle is available whether it is used or not: the added energy costof this atomization is zero.

Since the fuel outlet to the engine, nozzle 13, is at the varyingpressure of chamber 5, fuel flow for a given control setting would varywith manifold pressure in chamber 5 unless the control were pressurecompensated. However, constant pressure drop fuel metering assembly 17aassures that fuel flow is invariant with outlet pressure variations.Fuel pressurized at pump 18 is divided between fuel bypass circuit 18aand engine fuel control valve 17 by the interaction of needle valveassembly 19 with diaphragm 23 and spring 22 which assures that thepressure drop across diaphragm 23, and hence the pressure drop acrossvalve 17, is a constant pressure drop dependent on the force ofspring 22on diaphragm 23. The use of bypass control systems to control the fluidpressure across a metering valve, as in assembly 17a, is well known tothe fluid control art.

Fuel flow through valve 17 is therefor a unique function proportional tovalve orifice cross section of this valve. Assuming that valve 17 is todesigned that its flow is linear with its control position, the controlof valve 17 is to be linked to open and close proportionately with thex-opening of x-plates 3, 4 (linkage not shown). With this proportionallinkage combined with the y-opening proportional to h(IMV),/g(IMV), thesystem of FIG. 2 gives the desired air-fuel metering characteristics.

Various techniques can be used to change the constant of proportionalitybetween fuel flow and throttle x-opening as a function of parameterssuch as barometric pressure, engine temperature, intake air temperature, etc., as previously described. Both the x control linkage and thelinkage to valve 17 can be combined in a common radius arm, and theradius of one or both of the actuator points can be made to change as adesired function of correction parameters. Alternatively, the springforce of spring 23 can be varied, for instance by a, servo controlledscrew thread, to vary the pressure drop Ap across valve 17.'Fuel flowwill vary as the square root of Ap. Various other proportioning linkagesbetween the fuel control and throttle x-opening control are obvious tothose skilled in the arts of mechanics and linkages.

FIG. 3 shows the position of rectangular iristhrottle plates such asthose of FIG. 2 on the manifold 5 where the distance between plates 1and 2 forms the yopening and the distance between plates 3 and 4formsthe x-opening of the iris throttle. Where the fuel outlet I ispositioned directly below the air throttle in the high velocityairstream to secure fuel atomization it is important that the fueloutlet remain in the center of the airflow opening as the throttle opensand closes to promote fuel distribution. If the fuel input did notutilize the airstream for atomization, a throttle geometry with a movingthrottle area center could be used.

FIGS. 3a, 3b, 3c and 3d show some examples of plate slidingpatterns toproduce the desired pressure compensated area of the invention.

FIG. 3a shows a mounting where four plates slide apart and together toform rectangle iris opening with sides proportional to x and y. Thedistance between one pair of parallel plates formsthe x-opening; thedistance between the other pair of parallel plates forms the yopening.

FIG. 3b shows a throttle with an opening which'is also.

and the other perpendicularsides move to adjust the x' and y opening asrequired.

FIG. 30 shows a throttle assembly analogous to that of FIG. 3a, but herethe opening is a parallelogram. The throttle opening of 3c will beproportional to x times y, as desired, so long as the sliding platesmaintain adjacent angles constant and slide open and closed inproportion to x and y.

FIG. 3d shows a throttle analogous to FIG. 3a, but where the slidingplates are curved on the throttling edges rather than straight. Thecurves as shown are probably more exaggerated than would be useful inpractice. Curving the plates rather than using straight lines can beuseful for two purposes: 1) small deviations from linearity on the edgesof the plate which forms the throttle opening when the throttle isrelatively closed can be used to correct for the small effect of airviscosity to produce more accurate air control, or 2) curved I platescan be used to bias h(IMV)/g(lMV) for certain ranges of engine operationif this is desired.

Other iris air throttles which can vary their area in proportion tomanifold vacuum as well as desired fuel flow can be designed: it isprobably impossible to list all the geometrically possibleconfigurations which could accomplish this. However, it is operationallyuseful for the airflow compensating function of a pressure compensatedairthrottle to be as described in this specification for automobilefuel-air control design.

FIG. 4 illustrates a linkage for a rectangular iris air throttle. Thislinkage operates two of the plates 50 (which are below the other twoplates 51 shown in dotted lines); the linkage that operates the otherpair of plates 51 would be similar and is not shown. The motion of theplates 50 is kept linear by the guides 59 when the pins 57 move in theslots 58. The pins 57 are actuated by the cross arms 52 pivoting onpivots 54. The pivots 54 are mounted on supports 53 which, with guides59, produce one-dimensional motion. The control arm 56 moves in responseto diaphragm 60 and actuates the cross arm 52 to which it is connectedby pivot 54a. The spring 61 is wound so that the distance between theplates 50 is proportional to the function h(lMV)/g(IMV) when the intakemanifold vacuum in chamber 49 acts on diaphragm 60. This diaphragmassembly is operationally similar to diaphragm assembly 12a shown inFIG. 2. A desirable knife edge shape for the plates 50 is illustrated inFIG. 4a.

In FIG. there is shown a linear fuel supply system comprising elements13, 14, 15, 16, l7, l8, 19 as in FIG.2 combined with a computer 65controlling circular iris air throttle 66 to form an engines air-fuelsupply system. The computer 65 senses engine conditions through sensors67, 68, 69, 70. These sensors sense a number of control parameters in amanner well known to the art. The computer 65 responds to sensedconditions and accordingly controls the iris air throttle 66 by means ofthe servomotor 64 and the gear linkage 63. The interaction of thecomputer 65 and the linear fuel supply system (l3, 14, 15, 16, 17, 18,19) produces the proper air-fuel ratio control for the engine connectedto intake manifold 62.

What is claimed is:

1. In an air-fuel control system for an internal combustion engine, thecombination comprising:

a. fuel flow control means for supplying fuel to the engine;

b. an air intake manifold operated at less than atmospheric pressure;

0. a source of air at atmospheric pressure;

d. an air throttle connected between said source of air and the intakemanifold for controlling airflow to said manifold, said air throttlehaving-a variable flow cross section area; and p e. means forcontrolling the variable flow cross section area wherein said means isresponsive to the fuel flow times afunction of the pressure drop betweenthe pressure at said air pressure source and the. pressure in the intakemanifold.

2. In an air-fuel control system for an internal combustion engine, thecombination comprising:

a. fuel flow control means for supplying fuel to the engine;

b. an air intake manifold operated at less than atmospheric pressure;-

c. a source of air at atmospheric pressure;

d. an air throttle connected between said source of air and the intakemanifold for controlling airflow to said manifold, said air throttlehaving a variable flow cross section area; and

e. means for controlling the variable airflow cross section area whereinsaid means varies the cross section proportional to the fuel flow timesa function of the pressure drop between the pressure of said source andthe pressure in said intake manifold. i

3. The invention as set forth in claim 2 and wherein .the variable flowcross section area comprises a variable opening formed by adjustableinwardly extending closure members.

4. The invention as set forth in claim 2 and wherein the variable flowcross section comprises a rectangular opening formed by adustableinwardly extending closure members.

5. The invention as set forth in claim 4 and wherein the adjustableinwardly extending closure members move in response to the fuel flow andto a function of e width of the opening in proportion to fuel flow andthe height of the opening as a function of the pressure differencebetween atmospheric pressure and that in the intake manifold.

7. The invention as set forth in claim 3 and wherein the means forcontrolling the adjustable inwardly extending closure members comprisesa spring diaphragm control linkage responsive to the pressure dropbetween the pressure of said source and the pressure in said intakemanifold. V I

8. A method for controlling the air-fuel ratio in an internal combustionengine, said method comprising the steps of:

a. controlling the flow of fuel to the engine,

b. operating the intake manifold at a pressure less than atmospheric,

c. feeding air to the manifold from a source of atmospheric pressureair, and

d. controlling the airflow cross sectional area between the source ofatmospheric pressure air and the intake manifold to vary said area inproportion to fuelflow times a function of the pressure differencebetween said manifold pressure and atmospheric pressure.

9. A method for controlling the air-fuel ratio in an internal combustionengine, said method comprising the steps of:

a. operating the intake manifold at a pressure less than atmospheric,

b. controlling the flow of fuel to the engine independently of thepressure of said intake manifold,

c. feeding air to the intake manifold from a source of atmosphericpressure air, and

d. controlling the airflow cross sectional area between said intakemanifold and said source of atmospheric pressure air as a function offuel flow a and the pressure difference between said manifold pressureand atmospheric pressure.

1. In an air-fuel control system for an internal combustion engine, thecombination comprising: a. fuel flow control means for supplying fuel tothe engine; b. an air intake manifold operated at less than atmosphericpressure; c. a source of air at atmospheric pressure; d. an air throttleconnected between said source of air and the intake manifold forcontrolling airflow to said manifold, said air throttle having avariable flow cross section area; and e. means for controlling thevariable flow cross section area wherein said means is responsive to thefuel flow times a function of the pressure drop between the pressure atsaid air pressure source and the pressure in the intake manifold.
 2. Inan air-fuel control system for an internal combustion engine, thecombination comprising: a. fuel flow control means for supplying fuel tothe engine; b. an air intake manifold operated at less than atmosphericpressure; c. a source of air at atmospheric pressure; d. an air throttleconnected between said source of air and the intake manifold forcontrolling airflow to said manifold, said air throttle having avariable flow cross section area; and e. means for controlling thevariable airflow cross section area wherein said means varies the crosssection proportional to the fuel flow times a function of the pressuredrop between the pressure of said source and the pressure in said intakemanifold.
 3. The invention as set forth in claim 2 and wherein thevariable flow cross section area comprises a variable opening formed byadjustable inwardly extending closure members.
 4. The invention as setforth in claim 2 and wherein the variable flow cross section comprises arectangular opening formed by adustable inwardly extending closuremembers.
 5. The invention as set forth in claim 4 and wherein theadjustable inwardly extending closure members move in response to thefuel flow and to a function of the pressure difference betweenatmospheric pressure and that in the intake manifold.
 6. The inventionas set forth in claim 3 and wherein the variable opening is aparallelogram having a width and height, wherein said (closure) memberscontrol the width of the opening in proportion to fuel flow and theheight of the opening as a function of the pressure difference betweenatmospheric pressure and that in the intake manifold.
 7. The inventionas set forth in claim 3 and wherein the means for controlling theadjustable inwardly extending closure members comprises a springdiaphragm control linkage responsive to the pressure drop between thepressure of said source and the pressure in said intake manifold.
 8. Amethod for controlling the air-fuel ratio in an internal combustionengine, said method comprising the steps of: a. controlling the flow offuel to the engine, b. operating the intake manifold at a pressure lessthan atmospheric, c. feeding air to the manifold from a source ofatmospheric pressure air, and d. controlling the airflow cross sectionalarea between the source of atmospheric pressure air and the intakemanifold to vary said area in proportion to fuel flow times a functionof the pressure difference between said manifold pressure andatmospheric pressure.
 9. A method for controlling the air-fuel ratio inan internal combustion engine, said method comprising the steps of: a.operating the intake manifold at a pressure less than atmospheric, b.controlling the flow of fuel to the engine independently of the pressureof said intake manifold, c. feeding air to the intake manifold from asource of atmospheric pressure air, and d. controlling the airflow crosssectional area between said intake manifold and said source ofatmospheric pressure air as a function of fuel flow and the pressuredifference between said manifold pressure and atmospheric pressure.